level 9 is definitely the hardest. difficulty is based on where you place units on first move DO NOT place a unit on front row next to hill whatever you do. this pisses ai off big time. Level 9 is my fav now. use leviatin to block left side. It can take direct hit from tank and anti aircraft tank. you must be defensive for roughly 20 rounds. Use the choke pts and repair tanks. I can do this level by building 9 units with no lost units, not everytime but that is my record
 "Kingdom Rush Frontiers"){kind=icon}
 "Battalion: Nemesis"){kind=icon}